Why is the ocean blue?

_Elsa_

Andrew has finished eating his candy and now wants to know why the ocean is blue. Olivia has no problem giving him some facts on this but isn’t sure if it might be over his head.

‘First, we need to know some fun facts about the nature of light. The light we see, which we call white light, is made up of incredibly tiny particles called photons. A photon is even smaller than an atom. You can’t see them, but they’re there. These particles are very strange because when we measure them, sometimes they move like a tiny ball and sometime like a wave – weird, right? 

White light is made from photons that have many different wavelengths, some shorter and some longer, and together make up all the colours of the rainbow. The photons with the shortest wavelength we can see look blue, while those with the longest wavelength look red. 

Now that we know a bit more about light, we can begin to answer your question. Experiments have shown that pure water (water with nothing else dissolved in it) absorbs more of the red light than the blue light. But how much of the red light will get absorbed? Well, that depends on how much water the light has to pass through.

You might be wondering why the water in a glass looks clear. It is because the glass of water is too small to absorb more red light waves. To see the effect with your eye, you would have to look through a glass of water as big as a swimming pool. That amount of water could absorb quite a lot of red light, so the water would look quite blue. 

Now imagine a glass that held an entire ocean’s worth of water. It would be enormous! With that much water, you could absorb a LOT of red light. So it would look very blue.  

We know the sky is blue and the sea does reflect some of this light. So, yes, it does play a role. 

To sum it all up: the sea is blue because of the way water absorbs light, the way particles in the water scatter light, and also because some of the blue light from the sky is reflected. 

Finally, we need to think about the time of day and the position of the Sun in the sky. When the Sun is shining bright, the sea appears bluer than it does late at night, when the sea looks very dark and almost black.’ (Source) 

Let’s continue - Olivia looks for a video to help Andrew understand it better

Start at the beginning – Olivia explains the colors of the sky

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Start at the beginning of the main story – Why … But WHY?

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